The present invention relates to the production of holograms, and specifically concerns a method and apparatus for producing stereographically correct, temporally coherent, full color hologram images.
Conventional methods of producing holograms derived from a two-dimensional image or pattern which is resolvable into a three-dimensional image often involve the obtaining of a photographic image of a subject using a single camera mounted on a rail for linear movement. The rail is positioned a desired distance from the subject so that the subject is located approximately midway between the ends of the rail. As the camera moves along the rail from one end to the other, a sequence of exposures of different views of the subject is taken. These exposed images are then sequentially projected by a source of coherent light upon an H1 plate in the presence of a reference beam to obtain an H1 hologram. The H1 is subsequently transferred to an H2 plate for completion of the hologram.
A significant disadvantage of this method of obtaining multiple views of the subject is that the exposures are temporally incoherent. In other words, because the images were taken at different times, a margin of error is introduced into the photographic process, whereby different lighting conditions, vibration of the camera as it moves along the rail, or slight movement of live subjects may cause some distortion of the final H1 image.
Another disadvantage of conventional holographic rail camera systems is that the movement of the camera along the rail requires the camera to be set at a faster shutter speed to avoid "image smear". Further, artificial lighting is often required to accommodate the faster shutter speed. Thus, the actual lighting conditions of the subject cannot be reproduced by existing rail camera systems.
Yet another disadvantage of conventional stereograph holographic systems is that when the sequence of exposed photographic images of the subject is projected upon an H1 plate using a conventional optical printing system, a single wavelength of laser light is used as the source of coherent light. Thus, even if color film were used in the conventional rail camera in photographing the subject, the single wavelength laser light source would produce a monochromatic H1 image. When a color hologram is desired, the color is derived through a multi-step color separation under white light illumination. This process results in distortions in the colors and in the alignment of the images, some of which cannot be optically removed. Further, the linear movement of the rail camera precludes the production of a truly stereographically correct final hologram.
Thus, there is a need for a holographic production system in which an instantaneous, point-in-time sequence of images of a subject is produced to result in a temporally coherent, stereographically correct hologram. There is also a need for a holographic production system capable of producing an original full color holographic image of a subject in its naturally lit environment.